Atomic Weight

The average weight of an atom of an element.

Binding Medium

The vehicle in which pigments are suspended to create paint. Examples include: drying oil, egg tempera, plant gum, animal glue, and modern synthetics such as acrylic polymers.


A layer applied to a support to prepare it for painting. The ground consists of a binding medium and filler and may be either white or colored.

Electromagnetic Radiation

A term that refers to the link between electricity and magnetism first described by James Clerk Maxwell in 1865. Using mathematics to explain the link Maxwell showed that when an electric current moves backward and forward, it creates electromagnetic waves that radiates outward at the speed of light. From this discovery Maxwell concluded that light itself is a form of electromagnetic wave. The various types of electromagnetic radiation are distinguished by their wavelengths. They include: radio, television, radar, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays, and cosmic rays. With the exception of visible light, all forms of electromagnetic radiation are invisible to humans.

Electromagnetic Spectrum

A spectrum of wave energy that includes: radio, television, radar, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays, and cosmic rays.


A form of electromagnetic radiation with wavelengths longer than visible light. Located just beyond red in the electromagnetic spectrum, infrared waves are generated by objects that produce heat, such as human beings or an incandescent light.

Infrared Reflectography (IRR)

A term coined by J. R. J. van Asperen De Boer in the late 1960s to describe a technique for viewing the underdrawing and early paint stages of a painting using cameras equipped with infrared-sensitive detectors. Related to infrared photography, infrared reflectography allows greater penetration of the paint layers by using wavelengths of infrared radiation that are slightly longer than those used in infrared photography. Combined with advanced optics, detectors, and digitization equipment, a clearer image of underlying paint layers and drawing is achieved. Reflectography refers to the light reflecting off the surface of the ground and into the camera lens.


Consists mainly of powdered pigments combined with a binding medium.


The coloring materials in paint. They can be found in the natural world and/or synthesized in the laboratory and are derived both from organic and inorganic sources.

Raking Light

A light placed at an angle to an object in order to make its surface texture more readily visible.


The structure on which a picture is painted. Materials used include canvas stretched over a wooden frame or solid materials such as wood, glass, metal, stone, and various architectural surfaces.


The initial sketch made by an artist prior to applying paint layers. The underdrawing may be very detailed or may consist of brief visual notations. Drawing may be applied directly to the ground or may be transferred from an existing sketch using a variety of methods.

Ultraviolet (UV)

A form of electromagnetic radiation with wavelengths just shorter than visible light and just longer than x-rays. Located just below violet in the electromagnetic spectrum, ultraviolet radiation has greater energy than visible light.


A transparent coating applied to the surface of a completed painting to protect the paint layer and provide a uniform surface gloss. Traditional varnishes consist of a natural resin dissolved in a volatile solvent or drying oil. Modern synthetic varnishes are made of chemically synthesized resins dissolved in an appropriate solvent.


A form of electromagnetic radiation with very short wavelengths. X-rays are high energy and capable of penetrating solids to varying degrees depending on the atomic weight of the object. The higher the atomic weight the more difficult it is to penetrate the object with x-rays. X-rays can be recorded on photographic film.